Single-Shaft Eccentric Screw Pump

ABSTRACT

A double/triple-thread single-shaft eccentric screw pump is provided. The rotor of the pump overhangs little in comparison with the flange type connecting structure. The whole length of the pump is short, and the pump casing of the pump is short and small in diameter, so that the pump is small in size and light in weight. One end of a flexible rod is tapered and has a tapped hole formed at its axis. One end of the rotor has a tapered bore formed at its axis, into which the tapered end of the flexible rod is fitted. The rotor has a through bore formed at its axis, through which a tension bolt extends from the other end of the rotor. The tension bolt has a front threaded end, which is screwed into and fastened to the tapped hole of the flexible rod.

FIELD OF THE INVENTION

The present invention relates to the structure for connecting theflexible rod, which is mainly metallic, to the drive shaft of the driveunit or the rotor in a single-shaft eccentric screw pump. Specifically,the invention relates to a single-shaft eccentric screw pump having apump body and a flexible rod. The pump body includes an externallydouble-threaded rotor elliptic in section and a stator having aninternally triple-threaded hole in the shape of a substantiallyequilateral triangle in aperture section. The pump rotor engages withthe triple-threaded hole. The flexible rod couples the pump rotor andthe drive shaft of a drive unit together.

BACKGROUND OF THE INVENTION

In general, a single-shaft eccentric screw pump has a pump bodyincluding an internally double-threaded stator and an externallysingle-threaded rotor. The pump stator has a longitudinally tapped holeelliptic in section. The pump rotor is circular in section, and itsthread pitch is ½ of the thread pitch of the tapped hole. The pump rotoris in slidably rotatable engagement with the tapped hole and creates apumping action by revolving eccentrically around the axis of revolutionin the pump stator, rotating on its own axis while revolving in theopposite direction around the axis of revolution. The pump rotor and thedrive shaft of a drive unit are coupled by a coupling rod. In general, ameans is adopted for allowing the pump rotor to revolve eccentricallywith a universal joint interposed between the rotor and the couplingrod, or with a flexible and relatively long coupling rod used betweenthe rotor and the drive shaft.

If the coupling rod is a metallic flexible rod, it is proposed oradopted that the rod be or is connected to the pump rotor or the driveshaft by means of flanges (refer to the connection between the flexiblerod 6 and drive shaft 42 in FIG. 4). One end of the flexible rod istapered and has a hole tapped in it. A connecting casing has an outwardflange formed around it and a tapered bore formed in it, into which thetapered end of the flexible rod is fitted. A bolt extends through theend of the connecting casing, is screwed into the tapped hole of theflexible rod, and is tightened to fix the rod and the casing together. Ajoint case has an inward flange formed at its front end and a tighteningring formed at its rear end. The inward flange engages with the outwardflange of the connecting casing. The pump rotor or the drive shaft has astep formed at one of its ends. The tightening ring engages with the endstep, supports it, and is tightened to fix the connecting casing and thepump rotor or the drive shaft together.

A single-shaft eccentric screw pump disclosed as a prior art has a rotorand a drive shaft, which are coupled together by a flexible rod made ofengineering plastic. One end of the flexible rod may be tapered. One endof the drive shaft may have a tapered bore. The tapered end may befitted into the tapered bore and bonded to it with an adhesive.Otherwise, one end of the flexible rod and one end of the drive shaftmay have a key and a key groove, which connect the ends together. Forthis art, reference may be made to JP H9-264264 A (paragraphs 0013,0016, and 0018, and FIGS. 8 and 9).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The conventional single-shaft eccentric screw pump in which the rotor orthe drive shaft is connected to the flexible rod by means of flanges hasthe following problems.

Because the pump is fitted with a flanged connecting casing and aflanged joint case, the number of parts of the pump is large, and thepump is complicated in structure.

In order to inspect and replace the mechanical seal etc. of the pump, itis necessary to remove the bearing in the bearing casing of the pump.This results in complicated disassembly and assembly.

The formation of the flanges lengthens the pump.

The rotor might have a tapered bore formed at one of its ends. The otherend of the flexible rod might be tapered and fitted into the taperedbore of the rotor. A tension bolt might extend through the rotor fromthe other end of the rotor. The tension bolt has a front threaded end,which might be screwed into the tapered end of the flexible rod so as toconnect the rod and the rotor. In this case, if the pump is a generalsingle/double-thread single-shaft eccentric screw pump as describedabove, the rotor would be long, and its eccentricity would be great. Therotor of this pump could have a through bore for the tension bolt. Thediameter of the through bore would be limited to a small value. Thiswould make it impossible to secure sufficient thread strength forconnection with the flexible rod.

The connecting structure disclosed in the foregoing Japanese publicationis not sufficient in connecting strength if a metallic flexible rod isconnected to the drive shaft by means of bonding or keying.

In view of the foregoing points, the object of the present invention isto provide a double/triple-thread single-shaft eccentric screw pump inplace of a general single-shaft eccentric screw pump as described above.The double/triple-thread single-shaft eccentric screw pump has aninternally triple-threaded stator and an externally double-threadedrotor. Because this pump is high in pressure resistance, the rotor canbe short. Because the eccentricity of the rotor is small, the throughbore which can be formed through it for a tension bolt can be large indiameter so that the bolt can fasten the rotor with sufficient threadstrength. In comparison with the flange type connecting structure, therotor overhangs little. The whole length of this pump is short. The pumpcasing of this pump is short and small in diameter. The mechanical sealof this pump is simple to disassemble and assemble. It is easy to makethis pump small in size and light in weight. At least one end of theflexible rod of this pump has a taper-stop tension bolt type connectingstructure, which is mechanically stronger than a bonding or keying typeconnecting structure.

Means for Solving the Problems

In order to achieve the foregoing object, a single-shaft eccentric screwpump according to the present invention comprises a pump body, a pumpcasing, and a flexible rod, the pump body including an externallydouble-threaded rotor elliptic in section and a stator having aninternally triple-threaded bore in the shape of a substantiallyequilateral triangle in aperture section, the rotor being in engagementwith the stator bore, the flexible rod coupling the rotor and a driveshaft together, the drive shaft being connected to a drive unit, thesingle-shaft eccentric screw pump being characterized by: the flexiblerod being tapered at least one of its ends, the tapered end having atapped hole formed at its axis; the rotor or the drive shaft having atapered bore formed at its axis, the tapered end being fitted into thetapered bore; the rotor or the drive shaft further having a through boreformed at its axis; a tension bolt extending through the through borefrom the other end of the rotor; and the tension bolt having a frontthreaded end, the threaded end being screwed into and fastened to thetapped hole in the tapered end of the flexible rod so as to connect therod and the rotor or the drive shaft together.

As described above, the pump body includes an externally double-threadedrotor and an internally triple-threaded stator. This enables the pump tobe shorter than a conventional single-shaft eccentric screw pump havingan externally single-threaded rotor and the same discharge rate. Thisalso enables the through bore of the rotor to be large in diameter, sothat the engaging parts of the rotor and tension bolt can havesufficient thread strength. Accordingly, not only the drive shaft butalso the rotor can be connected by a taper-stop tension bolt. Incomparison with the conventional flange type, the rotor or the driveshaft does not need to have a protrusion formed at an end of it, towhich a flange would be fixed. Accordingly, the rotor or the drive shaftoverhangs little, so that it is possible to minimize the bending momentexerted from the flexible rod particularly on the rotor. This improvesthe discharging performance of the pump. Because the rotor or the driveshaft has no flange and needs to have no protrusion or the like forengaging with a flange, the pump is simple in structure. This makes iteasy to disassemble and inspect the mechanical seal in the pump. Thisalso makes it easy for the pump to be small in size and light in weight.

As described in claim 2, the flexible rod may be tapered at both itsends. Each of the tapered ends has a tapped hole formed at its axis.Each of the rotor and the drive shaft may have a tapered bore formed atits axis. One of the tapered ends of the flexible rod is fitted into thetapered bore. Each of the rotor or the drive shaft may further have athrough bore formed at its axis. A first tension bolt may extend throughthe through bore of the rotor from the other end of the rotor. A secondtension bolt may extend through the through bore of the drive shaft fromthe other end of the rotor. Each of the tension bolts has a frontthreaded end, which is screwed into and fastened to the tapped hole inone of the tapered ends of the flexible rod so as to connect the rod tothe rotor and the drive shaft.

In the single-shaft eccentric screw pump described in claim 2, both endsof the flexible rod are connected to the drive shaft and the rotor bytaper-stop tension bolts. Accordingly, the drive shaft and the rotorneed to have no flange. This makes the pump simple in structure andenables the pump casing to be smaller in diameter, making it easy forthe pump to be small in size and light in weight.

As described in claim 3, the first tension bolt may further have a rearthreaded end, which engages with a nut. It is preferable that a coverfor covering the nut be fitted to the end of the rotor which is awayfrom the flexible rod.

In the single-shaft eccentric screw pump described in claim 3, the covercovers the nut and the rear threaded end of the first tension bolt. Thecover keeps the nut and this bolt end out of contact with the liquidbeing transferred. This prevents the nut and the parts adjoining it fromcorroding. Accordingly, the pump can be used stably for a long period oftime.

As described in claim 4, one end of the flexible rod may be connected toa central portion of the rotor or a central portion of the drive shaftat any point between both ends of the rotor or any point between bothends of the drive shaft.

In the single-shaft eccentric screw pump described in claim 4, theflexible rod may be connected to middle portions of the rotor and driveshaft. In this case, the load acting from the flexible rod through therotor on the stator is exerted on a middle portion of the stator. Thisuniformizes the load on the stator, thereby lengthening the life of thestator 22. The bending moment acting from the flexible rod on theadjacent end of the drive shaft is supported near the bearing, so thatthe load on the drive shaft is reduced. The pump casing is shortened, sothat the overall length of the pump is shortened. This saves space.Alternatively, the flexible rod may be connected to the ends of therotor and drive shaft which are away from the pump casing. This furthershortens the overall length of the pump. Depending on the properties ofthe liquid which the pump pumps, it is determined what portion of therotor or the drive shaft between both its ends should mostadvantageously be connected to the flexible rod.

ADVANTAGES OF THE INVENTION

As described above, the pump body of the single-shaft eccentric screwpump according to the present invention includes an externallydouble-threaded rotor and an internally triple-threaded stator. Thisenables the pump to be shorter than a conventional single/double-threadsingle-shaft eccentric screw pump having an externally single-threadedrotor and the same discharge rate. This also enables the through bore ofthe rotor to be large in diameter, so that, if the rotor and theflexible rod are connected by a taper-stop tension bolt, the engagingparts of the rotor and tension bolt can have sufficient thread strength.Accordingly, not only the drive shaft but also the rotor can beconnected by a taper-stop tension bolt. In comparison with the flangetype, the rotor or the drive shaft does not need to have an outwardflange formed at an end of it, to which another flange would be fixed.Accordingly, the mechanical seal is easy to disassemble and assemble. Inaddition, the rotor or the drive shaft overhangs little, so that thebending moment exerted from the flexible rod on the rotor or the shaftis minimized. This improves the discharging performance of the pump.

BEST MODE OF CARRYING OUT THE INVENTION

Embodiments of a single-shaft eccentric screw pump according to thepresent invention will be described below with reference to thedrawings.

FIG. 1 is a sectional view of an embodiment of a single-shaft eccentricscrew pump. FIG. 2 is an enlarged sectional view of an end portion ofthe rotor shown in FIG. 1. FIG. 3 is a view in the direction A in FIG.2.

As shown in FIG. 1, the single-shaft eccentric screw pump 1 of thisembodiment includes a pump body 2, a pump casing 3, a bearing unit 4, adrive motor (not shown), and a drive shaft 42. The pump body 2 is fittedat one end (on the left side in FIG. 1) of the pump 1. The pump casing3, bearing unit 4, and drive motor are arranged in order. The driveshaft 42 protrudes from the other end of the pump 1. The drive motor iscoupled to the drive shaft 42 and drives the pump 1.

The pump body 2 consists principally of an externally double-threadedrotor 21 elliptic in section and a stator 22 having an internallytriple-threaded hole 23 in the shape of a substantially equilateraltriangle in aperture section. The rotor 21 rotates in one direction(clockwise in FIG. 5) on its axis O in the triple-threaded hole 23, withthe axis O revolving eccentrically (FIG. 5) in the opposite direction(counterclockwise in FIG. 5) around the axis N of the stator 22. Thispumps a material in one direction through the spaces X (FIG. 5) betweenthe rotor 21 and the sides of the triple-threaded hole 23. Theeccentricity e of the rotor axis O from the stator axis N is as small as⅔ of that of a conventional single/double-thread single-shaft eccentricscrew pump. The discharge rate of the single-shaft eccentric screw pump1 is about 1.5 times as high as that of a single/double-threadsingle-shaft eccentric screw pump of the same outer diameter (andlength).

The front end of the stator 22 is fitted with an end stud 24 as adischarge port 24 a (in this embodiment) or a suction port. The stator22 is surrounded by a cylindrical stator casing 25, which is held by theend stud 24 and pump casing 3.

The pump casing 3 includes a bearing casing 41 formed as an extension atits other end. The pump casing 3 has a suction port 31 formed at its topnear the bearing casing 41. The suction port 31 opens upward, rightward,or leftward and is surrounded integrally by an outward flange 32. Thedrive shaft 42 is supported rotatably by a left bearing 43 and a rightbearing 44 in the bearing casing 41 and protrudes from this casing. Theouter diameter of the drive shaft 42 increases by three steps leftwardin FIG. 1. The drive shaft 42 includes a large diameter part 42L, amedium diameter part 42M, and a small diameter part 42S in rightwardorder in FIG. 1. One end (adjacent to the bearing casing 41) of the pumpcasing 3 is open. An annular support housing 11 is fitted to the insideof the open end 33 of the pump casing 3 and surrounds the large diameterpart 42L of the drive shaft 42. The large diameter part 42L issurrounded by mechanical seals 12, between which the support housing 11is positioned. The mechanical seals 12 prevent the liquid beingtransferred from leaking out of the pump casing 3 into the bearingcasing 41.

The rotor 21 and drive shaft 42 are coupled by a metallic flexible rod6, which is made of titanium alloy or stainless steel in thisembodiment. As shown in FIG. 1, the ends 61 of the flexible rod 6 areslightly thick and tapered. Each tapered end 61 has a threaded hole 62formed in its center for engagement with the front threaded end 71 of atension bolt 7, which will be described later on.

In this embodiment, the flexible rod 6 is connected to each of the rotor21 and drive shaft 42 by a taper-stop tension bolt. Specifically, therotor 21 has a through bore 21 a formed through it along its axis forthe tension bolt 7. Likewise, the drive shaft 42 has a through bore 42 aformed through it along its axis for a tension bolt 7′. The tensionbolts 7 and 7′ have front threaded ends 71 and 71′ respectively and rearthreaded ends 72 and 72′ respectively, all of which are smaller in outerdiameter than the main bodies of the tension bolts 7 and 7′. The rearthreaded ends 72 and 72′ are slightly larger in outer diameter than thefront threaded ends 71 and 71′ respectively.

The rotor 21 has a tapered bore 21 b formed in its end adjacent to thepump casing 3. One tapered end 61 of the flexible rod 6 is fitted intothe tapered bore 21 b. The tension bolt 7 is inserted from the other endof the rotor 21. The front threaded end 71 of the tension bolt 7 isscrewed into the threaded hole 62 of the flexible rod 6, with a washer 8interposed. The tension bolt 7 is then tightened to be fixed to theflexible rod 6.

As shown in FIG. 2, the rear threaded end 72 of the tension bolt 7engages with a nut 10, with a washer 9 interposed, which consists of asmall diameter part 9 a and an outward flange 9 b formed integrallyaround this part. The small diameter part 9 a can be inserted into thethrough bore 21 a of the rotor 21. The nut 10 is tightened to fix therotor 21 and flexible rod 6 together. A cover 26 in the form of a hat isfixed to the end of the rotor 21 by set screws 27 and covers the nut 10and washer 9. The rotor 21 has a pair of steps 21 c formed at its endopposite each other. The steps 21 c are spaced from the end of the rotor21. As shown in FIG. 3, each step 21 c has an engaging hole 21 d forengagement with a part of a tool (not shown) for keeping the rotor 21from rotating.

Likewise, the drive shaft 42 has a tapered bore 42 b formed in its endadjacent to the pump casing 3. The other tapered end 61 of the flexiblerod 6 is fitted into the tapered bore 42 b. The tension bolt 7′ isinserted from the other end of the rotor 42. The front threaded end 71′of the tension bolt 7′ is screwed into the threaded hole 62 of theflexible rod 6, with a washer 8 interposed. The tension bolt 7′ is thentightened to be fixed to the flexible rod 6. The rear threaded end 72′of the tension bolt 7′ engages with a nut 10, with a washer 9interposed, which consists of a small diameter part 9 a and an outwardflange 9 b formed integrally around this part. The small diameter part 9a can be inserted into the through bore 42 a of the drive shaft 42. Thenut 10 is tightened to fix the drive shaft 42 and flexible rod 6together. The nut 10 and washer 9 on the tension bolt 7′ are not coveredbecause this nut 10 and other parts adjacent to the drive shaft 42 areexposed to the atmosphere and kept out of contact with the liquid beingtransferred. The protruding end part of the drive shaft 42 is fittedwith a connecting key 42 c for connection with the drive motor (notshown).

A description will be provided below of how the single-shaft eccentricscrew pump 1 of Embodiment 1 operates.

With reference to FIG. 1, the drive motor rotates the drive shaft 42 ina specified direction. The torque of the drive shaft 42 is transmittedthrough the flexible rod 6 to the rotor 21, rotating the rotor 21 on theaxis O while revolving it eccentrically in the triple-threaded hole 23of the stator 22. The eccentricity of the rotor 21 from the stator 22 isabsorbed by the deformation of the flexible rod 6. This creates apumping action in the pump body 2, sucking liquid through the suctionport 31 into the pump casing 3, forcing it through the body 2, anddischarging it through the discharge port 24 a at the end stud 24. Ifthe drive motor (not shown) were rotated in the opposite direction,liquid would be sucked through the discharge port 24 a at the end stud24 and the pump body 2 into the pump casing 3 and discharged through thesuction port 31.

One embodiment of the single-shaft eccentric screw pump of the presentinvention has been described above and may be modified as follows.

In the single-shaft eccentric screw pump 1 of the foregoing embodiment,only the flexible rod 6 and drive shaft 42 could be coupled together bymeans of flanges. FIG. 4 shows the single-shaft eccentric screw pump 1′of another embodiment of the present invention. The pump 1′ includes asubstantially cylindrical connector 15 and a tightening ring 16. Theconnector 15 has a tapered bore 42 b for one tapered end 61 of aflexible rod 6. The connector 15 further has an outward flange 15 aformed around a middle portion of it. The tightening ring 16 has aninward flange 16 a formed at its front end. The tapered end 61 is fittedinto the tapered bore 15 b of the substantially cylindrical connector16. A short headed tension bolt 17 is inserted through the rear opening15 c of the connector 15. The front threaded part 17 a of the tensionbolt 17 is screwed into the threaded hole 62 of the flexible rod 6 andtightened to fix the rod 6 and connector 15 together. With the inwardflange 16 a engaging with the outward flange 15 a of the connector 15,the tightening ring 16 may tighten it around the step 42 d formed at anend of the drive shaft 42, so that the flexible rod 6 can be connectedto the drive shaft 42 rotatably with it. Otherwise, this embodiment issimilar in structure to the foregoing embodiment. Therefore, the partsof this embodiment which are common to that embodiment are shown withthe same reference numerals, and the descriptions of these parts areomitted. In this case, the formation of the flanges results in the pump1′ being longer, and they protrude radially, but the pumping operationof this embodiment is common to that embodiment.

FIG. 6 is a sectional view of a third embodiment of the single-shafteccentric screw pump according to the present invention. Thesingle-shaft eccentric screw pump 1-3 of this embodiment differs fromthe screw pump 1 of the first embodiment in that the tapered ends 61 ofthe flexible rod 6 of the pump 1-3 are connected to substantially middleportions of the rotor 21 and drive shaft 42.

As shown in FIG. 6, the rotor 21 has a circular long bore 27 formedbetween a central portion of its end face adjacent to the pump casing 3and a substantially middle point of the rotor 21. The rotor 21 furtherhas a tapered bore 27 b formed at the bottom of the long bore 27. Onetapered end 61 of the flexible rod 6 is fitted into the tapered bore 27b. A tension bolt 7 is inserted from a central portion of the other endface of the rotor 21. The front threaded end 71 of the tension bolt 7 isscrewed into the threaded hole 62 of the flexible rod 6, with a washer 8interposed, and is tightened to fix the rod 6 and the rotor 21 together.

Likewise, the drive shaft 42 has a circular long bore 45 formed betweena central portion of its end face adjacent to the pump casing 3 and asubstantially middle point of the shaft 42. The drive shaft 42 furtherhas a tapered bore 45 b formed at the bottom of the long bore 45. Theother tapered end 61 of the flexible rod 6 is fitted into the taperedbore 45 b. In this embodiment, the bearing unit 43 is positioned at thetapered end 61 (where the drive shaft 42 and flexible rod 6 areconnected). A tension bolt 7′ is inserted from a central portion of theother end face of the rotor 42. The front threaded end 71′ of thetension bolt 7′ is screwed into the threaded hole 62 of the flexible rod6, with a washer 8 interposed, and is tightened to fix the rod 6 and thedrive shaft 42 together. Otherwise, this embodiment is similar instructure to the foregoing embodiments. Therefore, the parts of thisembodiment which are common to those embodiments are shown with the samereference numerals, and the descriptions of these parts are omitted.

In the single-shaft eccentric screw pump 1-3 of this embodiment, theload acting on the stator 22 from the flexible rod 6 is exerted on amiddle portion of the stator 22. This uniformizes the load on the stator22, thereby lengthening the life of the stator 22. In this pump 1-3, thebearing unit 43 directly supports the bending moment acting on the endof the drive shaft 42 from the flexible rod 6. This reduces the load onthe drive shaft 42. The foregoing structure shortens the pump casing 3,thereby shortening the whole length of the pump 1-3, so that space issaved.

FIG. 7 is a sectional view of a fourth embodiment of the single-shafteccentric screw pump according to the present invention. Thesingle-shaft eccentric screw pump 1-4 of this embodiment differs fromthe screw pump 1-3 of the third embodiment in that the ends 61 of theflexible rod 6 of the pump 1-4 are connected to the ends of the rotor 21and drive shaft 42 which are away from the pump casing 3, and that oneend 61 of the rod is shrink-fitted or screwed to the rotor 21.

As shown in FIG. 7, the rotor 21 has a circular long bore 25 formedbetween a central portion of its end face adjacent to the pump casing 3and its other end. A plug 28 in the form of a hat is fitted into an endportion 25 a of the long bore 25 and has threaded holes 29 a. Bolts 29extend through an end of the rotor 21, are screwed into the threadedholes 29 a, and are tightened to screw the plug 28 to the rotor 21.Alternatively, the end portion 25 a of the long hole 25 might beinternally threaded, and the peripheral surface of the plug 28 might beexternally threaded so that the plug 28 could engage with the holeportion 25 a and be tightened to be connected to the rotor 21. The plug28 has a straight bore 28 b formed at its axis. The flexible rod 6 has acylindrical end 63, which is shrink-fitted into the straight bore 28 bso as to fix the rod 6 to the plug 28.

Likewise, the drive shaft 42 has a circular long bore 45 formed betweena central portion of its end face adjacent to the pump casing 3 and itsother end. The drive shaft 42 further has a tapered bore 45 b formed atthe bottom of the long bore 45. The tapered end 61 of the flexible rod 6is fitted into the tapered bore 45 b. A tension bolt 7″ is inserted froma central portion of the other end face of the drive shaft 42. The frontthreaded end 71″ of the tension bolt 7″ is screwed into the threadedhole 62 of the flexible rod 6, with a washer 8 interposed, and istightened to fix the rod 6 and the drive shaft 42 together. Otherwise,this embodiment is similar in structure to the foregoing embodiments.Therefore, the parts of this embodiment which are common to thoseembodiments are shown with the same reference numerals, and thedescriptions of these parts are omitted.

The pump casing 3 of the single-shaft eccentric screw pump 1-4 of thisembodiment is further shortened as compared with the single-shafteccentric screw pump 1-3 of the third embodiment, so that the wholelength of the pump 1-4 is minimized. Because the rotor 21 and flexiblerod 6 are connected by means of shrink fitting, the pump 1-4 is simplein structure. However, the flexible rod 6 and drive shaft 42 areconnected by the tension bolt 7′, which is tightened to securely couplethe rotor 21, the rod 6, and the shaft 42 together.

The positions where the ends of the flexible rod 6 are connected to thecentral portions of the rotor 21 and drive shaft 42 might not be limitedto those in the single-shaft eccentric screw pumps 1-3 and 1-4 of thethird and fourth embodiments. Depending on the properties (kind,viscosity, etc.) of the liquid which the pump 1-3 or 1-4 pumps, the endsof the flexible rod 6 could be connected to any (advantageous) portionof the rotor 21 between the ends of the rotor, and to any (advantageous)portion of the drive shaft 42 between the ends of the shaft. One end ofthe flexible rod 6 could be connected to the rotor 21 by means of notonly shrink fitting but also screws. The connection by means of shrinkfitting or screws might not be limited to the flexible rod 6 and rotor21, but could be applied to the rod 6 and drive shaft 42 as well. Inthis case, the flexible rod 6 would need to be connected to the rotor 21by a tension bolt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an embodiment of a single-shafteccentric screw pump according to the present invention.

FIG. 2 is an enlarged sectional view showing an end portion of the rotorshown in FIG. 1.

FIG. 3 is a view in the direction A in FIG. 2.

FIG. 4 is a sectional view showing a second embodiment of thesingle-shaft eccentric screw pump according to the present invention.

FIGS. 5( a)-5(f) are enlarged sectional views showing in order therotation and revolution of the rotor at a position in the stator of adouble/triple-thread single-shaft eccentric screw pump.

FIG. 6 is a sectional view showing a third embodiment of thesingle-shaft eccentric screw pump according to the present invention.

FIG. 7 is a sectional view showing a fourth embodiment of thesingle-shaft eccentric screw pump according to the present invention.

WHAT IS REPRESENTED BY REFERENCE NUMERALS

-   -   1, 1′, 1-3, 1-4: single-shaft eccentric screw pump    -   2: pump body    -   3: pump casing    -   4: bearing unit    -   6: flexible rod    -   7, 7′, 7″: tension bolt    -   8, 9: washer    -   10: nut    -   11: support housing    -   12: mechanical seal    -   15: substantially cylindrical connector    -   16: tightening ring    -   16 a: flange    -   17: headed tension bolt    -   22: stator    -   23: threaded hole    -   24: end stud    -   24 a: discharge port    -   25: stator casing    -   26: cover in the form of a hat    -   27, 45: long bore    -   28: plug in the form of a hat    -   31: suction port    -   41: bearing casing    -   42: drive shaft    -   61: tapered end    -   62: tapered bore    -   71, 71′, 72, 72′: threaded end

1. A single-shaft eccentric screw pump comprising a pump body, a pumpcasing, and a flexible rod, the pump body including an externallydouble-threaded rotor elliptic in section and a stator having aninternally triple-threaded bore in the shape of a substantiallyequilateral triangle in aperture section, the rotor being in engagementwith the stator bore, the flexible rod coupling the rotor and a driveshaft together, the drive shaft being connected to a drive unit, thesingle-shaft eccentric screw pump being characterized by: the flexiblerod being tapered at least one end thereof, the tapered end having atapped hole formed at an axis thereof; the rotor or the drive shafthaving a tapered bore formed at an axis thereof, the tapered end beingfitted into the tapered bore; the rotor or the drive shaft furtherhaving a through bore formed at the axis thereof; a tension boltextending through the through bore from the other end of the rotor; andthe tension bolt having a front threaded end, the threaded end beingscrewed into and fastened to the tapped hole in the tapered end of theflexible rod so as to connect the rod and the rotor or the drive shafttogether.
 2. The single-shaft eccentric screw pump as claimed in claim1, further characterized by: the flexible rod being tapered at both endsthereof, each of the tapered ends having a tapped hole formed at theaxis thereof; each of the rotor and the drive shaft having a taperedbore formed at the axis thereof, one of the tapered ends being fittedinto the tapered bore; each of the rotor and the drive shaft furtherhaving a through bore formed at an axis thereof; a first tension boltextending through the through bore of the rotor from the other end ofthe rotor; a second tension bolt extending through the through bore ofthe drive shaft from the other end of the rotor; and each of the tensionbolts having a front threaded end, the threaded end being screwed intoand fastened to the tapped hole in one of the tapered ends of theflexible rod so as to connect the rod to the rotor and the drive shaft.3. The single-shaft eccentric screw pump as claimed in claim 1, furthercharacterized by: the first tension bolt further having a rear threadedend; a nut engaging with the rear threaded end; a cover fitted to theend of the rotor which is away from the flexible rod; and the covercovering the nut.
 4. The single-shaft eccentric screw pump as claimed inclaim 1, further characterized in that one end of the flexible rod isconnected to a central portion of the rotor or a central portion of thedrive shaft at any point between both ends of the rotor or any pointbetween both ends of the drive shaft.
 5. The single-shaft eccentricscrew pump as claimed in claim 2, further characterized by: the firsttension bolt further having a rear threaded end; a nut engaging with therear threaded end; a cover fitted to the end of the rotor which is awayfrom the flexible rod; and the cover covering the nut.
 6. Thesingle-shaft eccentric screw pump as claimed in claim 2, furthercharacterized in that one end of the flexible rod is connected to acentral portion of the rotor or a central portion of the drive shaft atany point between both ends of the rotor or any point between both endsof the drive shaft.